This invention relates to battery technology. In particular, the invention relates to identifying battery type from voltage behavior in an electronic device.
Electronic devices capable of deriving operating power from one or more batteries are popular, widely available and in widespread use. Many of these electronic devices would be much less successful and even lose much of their market viability without the availability of reliable battery power. In particular, portable electronic devices generally depend on batteries as a primary power source. For example, popular portable electronic devices such as notebook and laptop computers, hand-held computers and personal digital assistants (PDAs), digital cameras, and cellular telephones would be of little or no use without battery power.
Electronic devices that employ batteries can use batteries as either a primary power source or as a secondary power source. In some cases the electronic device is powered entirely by a DC power supply based on a battery. In other cases, the battery powered electronic device can be operated either using battery power or using an external DC or AC power source. Generally, an AC adapter that converts the AC into DC provides the external DC power source for those electronic devices that use external DC power. The external AC/DC power source is also commonly used for recharging batteries in portable electronic devices that utilize in-situ rechargeable battery cells.
In simple terms, a battery is a device that converts chemical energy into electricity. A variety of battery types that have application to powering electronic devices are commercially available. Batteries can be divided into two broad classes depending on whether the battery is rechargeable or non-rechargeable. The distinction between rechargeable and non-rechargeable batteries is often important since attempting to recharge non-rechargeable batteries can lead to venting or leaking of electrochemical materials, and in extreme cases can result in dangerous explosions.
Directly related to whether or not a battery is rechargeable is the particular battery chemistry that is employed. The xe2x80x98chemistryxe2x80x99 of the battery refers to the specific combination of electrolytes and electrode materials used in the battery to create the chemical reaction that produces electrical power. Several battery chemistries, some of which produce rechargeable batteries and some of which produce non-rechargeable batteries, are in use and commonly available.
A common battery chemistry used for electronic devices is the well-known alkaline battery. The standard alkaline battery employs an alkaline gel, usually potassium hydroxide, as an electrolyte. The positive electrode is normally made of magnesium dioxide and the negative electrode is typically made of zinc. Other battery chemistries commonly used to power electronic devices include but are not limited to high-drain alkaline, high-energy lithium, nickel-metal hydride (NiMH) and nickel-cadmium (NiCd). Of these, normally only batteries having NiMH or NiCd chemistries are rechargeable while the others are generally not rechargeable. Batteries of different chemistries generally have different electrical properties such as open-circuit voltage, charge capacity, and peak current capacity. These electrical properties are a direct result of the characteristics of the chemical reactions taking place within the batteries. The unique characteristics of a chemical reaction such as rate, reaction path, and reactants involved are sometimes referred to collectively as the reaction""s xe2x80x98kineticsxe2x80x99.
Consumer batteries are most often classified based on the physical size and shape of the battery and only secondarily on chemistry and rechargeability. The physical size and shape of a battery is sometimes referred to as the xe2x80x98form-factorxe2x80x99 of the battery. Many battery chemistries are available in more than one form-factor. More to the point, some of the popular form-factors are available in more than one battery chemistry. Thus, even though different chemistries have different kinetics and rechargeability characteristics, the form-factor of the battery may not reflect any difference between them at all.
Electronic devices are available that utilize batteries having a wide variety of different form-factors. Both standard form-factors and custom form-factors are in common use. Available standard form-factors include but are not limited to AA, AAA, C and D cells. Many of the commercially available consumer battery chemistries can be found in more than one of the standard form-factors. Custom battery form-factors include customized single cells as well as specialized battery packs that contain more than one cell. A battery or battery pack having a customized form-factor is sometimes referred to as an xe2x80x98application-specificxe2x80x99 battery. Specialized application-specific battery packs and custom form-factors are most typically associated with battery chemistries that are rechargeable, though non-rechargeable battery types are available in some non-standard form-factors as well.
Most portable electronic devices monitor the battery during use and typically provide a charge level indicator or so-called xe2x80x98fuel gaugexe2x80x99 associated with battery life. The fuel gauge is intended to keep the user of the device apprised of the power remaining in the battery and, by extension, the probable remaining operating time of the electronic device. In addition, the fuel gauge is used by the device to determine a cut-off point in the battery discharge profile beyond which the device will cease to operate.
Fuel gauges on portable electronic devices generally attempt to xe2x80x98predictxe2x80x99 the power remaining based on measurements, usually voltage measurements, performed on the battery. Unfortunately, the accuracy of these measurements can and usually does depend on battery chemistry. For example, a voltage based fuel gauge calibrated for alkaline batteries will most likely not be accurate for NiMH batteries of the same form factor. Most portable electronic devices that can accept AA size batteries can utilize a variety of battery chemistries that are available in the AA form-factor. Unfortunately, as discussed hereinabove, the different battery chemistries do not behave the same way kinetically during discharge, especially in the presence of a short duration moderately high load. Thus, it is very difficult for conventional fuel gauging techniques to be accurate in high drain devices which can accept multiple battery chemistries and have no way of distinguishing one battery chemistry from another.
Most battery powered electronic products currently on the market use one of two methodologies in conjunction with monitoring batteries and providing fuel gauging. A first methodology known as current or power monitoring, determines the energy capacity remaining in a battery by monitoring the power or current passing into and out of the battery. This methodology requires knowledge of the approximate amount of energy that can be drained from the battery before it is discharged. As such, the use of power/current monitoring is generally restricted to electronic devices that utilize a battery where characteristics such as the battery chemistry and size are known a priori such as an application-specific battery pack. An application-specific battery pack is generally manufactured and distributed under the control of the electronic device manufacturer. Therefore, the manufacturer can impose limits on the battery pack specifications and thus effectively have a great deal of control over the accuracy of the battery monitoring and fuel gauging using the power/current monitoring methodology. Essentially, the fuel gauge can be calibrated accordingly based on the a priori knowledge of the application-specific battery pack performance characteristics.
Because a priori knowledge of battery characteristics is not possible in devices that accept multiple battery brands or chemistries, the power/current monitoring methodology generally is not used for fuel gauging in these devices. It is usually impossible to know with sufficient accuracy how much energy to expect from such a wide variety of battery types and/or from different manufactures of a given battery type. Therefore, for electronic devices that accept multiple battery types, especially multiple battery chemistries, an approach other than power/current monitoring is desirable.
A second methodology, most applicable to devices that utilize standard form-factor batteries such as AA cells, involves monitoring a change in voltage over a change in time (dv/dt) of the battery voltage during discharge. The change in voltage with respect to time is referred to as the voltage slope of the battery. If the voltage slope characteristics are known for a given battery type, a reasonable prediction can generally be made regarding power remaining based on a measured voltage at various points during the discharge cycle of the battery. Therefore, a periodic measurement of the battery voltage can be used to monitor the battery and provide a fuel gauge for the electronic device.
Unfortunately, the slope of the battery voltage during discharge is highly dependent on battery chemistry as well as peak and average discharge rates. Thus, conventional fuel gauges based on voltage monitoring are typically calibrated for the battery chemistry (e.g. alkaline) most commonly used in conjunction with the electronic device. The calibration of a fuel gauge for a particular battery chemistry yields good fuel gauge accuracy when using batteries of the calibrated chemistry. Conversely, the fuel gauge can report wholly erroneous results when a battery chemistry other than the one the gauge was calibrated for is used. For example, alkaline batteries have a fairly predictable sloping discharge profile and thus the methodology based on voltage monitoring works well with the alkaline battery chemistry. However, most non-alkaline batteries have a much flatter voltage discharge profile than alkaline batteries, making it difficult to detect any significant change in voltage until the battery is almost completely discharged. In other words, the scale used for voltage monitoring of alkaline batteries generally cannot be used as the scale for non-alkaline batteries without a significant reduction in fuel gauge accuracy.
Consider for example, a fuel gauge in an electronic device that has been calibrated for alkaline batteries using voltage monitoring. If lithium-iron disulfide batteries are used in the device instead of alkaline batteries, the fuel gauge that was calibrated for alkaline batteries will read the lithium-iron disulfide batteries as having 100% charge until the lithium-iron disulfide batteries are approximately 90% discharged. As another example, consider a device that uses voltage monitoring and that has been calibrated for NiMH batteries. If alkaline batteries are used instead of the NiMH batteries, the fuel gauge will report the alkaline batteries as being fully charged until they are approximately 80% discharged. Therefore, slope monitoring can be very inaccurate for chemistries other than the chemistry for which the device is calibrated.
Alkaline batteries are by far the most common battery type used in portable electronic products. As a result, most portable electronic products that employ the voltage monitoring fuel gauge methodology have fuel gauges that are calibrated for alkaline batteries. With the proliferation of alternative battery chemistries, such as lithium-iron disulfide and nickel metal hydride cells, and their relative availability to consumers, fuel gauges calibrated to alkaline batteries alone are becoming less accurate for many consumers. Consumers (electronic device users) are generally unaware of the very different voltage discharge behaviors among the various battery chemistries and often become frustrated with portable electronic devices when the battery gauge appears to be inaccurate. The end result of fuel gauge inaccuracy is that battery life is often sacrificed in favor of consistent device operation.
Thus, it would be advantageous to provide battery powered electronic devices with the ability to automatically identify the battery chemistry being used in the device. Such a device could adjust its fuel gauging system accordingly to provide more accurate information on battery life to the consumer or user. In addition, such a device could detect whether the battery is rechargeable or not and either enable or disable in-device charging. The device could also adjust the cutoff point used by the device for a particular chemistry to enable a given battery to be drained to an optimal discharge voltage level.
The present invention is a method and system of identifying battery chemistry of batteries in an electronic device by monitoring voltage behavior of the batteries in response to a stimulus. Advantageously, this method and system can perform the identification in the electronic device while the device is in normal operation without affecting the life of the battery or interfering with the user""s enjoyment of the electronic device. Moreover, the method and system of identifying battery chemistry of the present invention can be performed many times during the operation of the electronic device without compromising battery life or user enjoyment.
The method and system of the present invention provide for more accurate battery fuel gauging than conventional methods. The increased fuel gauge accuracy afforded by the battery chemistry identification method and system facilitates more effective use of the fuel gauge, including making a battery""s end-of-life more readily determinable and allowing for various battery chemistries to be drained to their optimal cutoff voltage. The method of the present invention is implemented in the electronic device by the system that monitors the voltage of a battery during normal use or operation of the electronic device.
In one aspect of the invention, a method of identifying battery chemistry of a battery in an electronic device by monitoring battery voltage recovery after removal of a known moderately high drain load is provided. The method comprises the steps of applying a moderately high load to a battery for a load period of time followed removing the load. Just as the load is removed, the voltage of the battery is monitored at time intervals that are shorter than the load period for a recovery time period. The battery chemistry of the battery is determined from voltage recovery with respect to time data obtained during the step of monitoring.
In another aspect of the invention, a method of identifying battery chemistry of a battery in an electronic device by monitoring voltage decline immediately after an application of a moderately high (or greater) load is provided. The method comprises the step of applying a moderately high load to a battery during a load period. Just as the load is applied, the voltage of the battery is monitored for a decline period at time intervals of less than the decline period. The battery chemistry of the battery is determined from voltage decline with respect to time data obtained during the step of monitoring.
In still another aspect of the invention, a method of identifying a battery chemistry of a battery in an electronic device is provided that monitors voltage decline immediately after an application of a moderately high (or greater) load, and then monitors voltage recovery after the load is removed. The method comprises the step of applying a moderately high load to a battery for a load period of time. Just as the load is applied, the voltage of the battery is monitored for a decline period at first time intervals that are less than the decline period. The method further comprises the step of measuring a first slope of the voltage during the load period from voltage decline data obtained in the step of monitoring. The method still further comprises the steps of removing the load and monitoring the voltage of the battery just after the load is removed for a recovery period at second time intervals that are less than the recovery period. A second slope of the voltage during the recovery period is measured from voltage recovery data obtained in the step of monitoring after the load is removed. The battery chemistry of the battery is determined from the measured first slope and the measured second slope data obtained in the steps of measuring.
In each of the methods, the battery chemistry determination is made by comparing the monitored or measured data to a set of predetermined reference values or ranges representing the responses of various battery chemistries to similar load conditions. The measured data in each method represent different electrical quantities related to aspects of the particular battery chemistry kinetics being measured. The step of determining comprises identifying a set of predetermined values that most closely match the measured data. The chemistry associated with the set of values that were identified is then chosen as the best guess for the battery chemistry. Any one of the above methods can be used independently.
In yet still another aspect of the present invention, a system that implements the method of the present invention in an electronic device is provided. The system eliminates the need to make compromises in designing a one-size-fits-all battery system for electronic devices. Further, the system automates the method of battery type identification in the electronic device during normal operation without the need for an artificial load that reduces the battery lifetime. The system comprises a monitoring subsystem to monitor or collect voltage data of an installed battery for a short period of time in response to a stimulus (load) and a calculation subsystem to calculate the slope of the battery voltage with respect to time and to make a best guess identification of the battery chemistry.
The method and system of the present invention allows for fuel gauging in the electronic device to be much more accurate than when the battery chemistry is not known a priori or the device is not calibrated for the particular chemistry. Importantly, the system can distinguish rechargeable battery chemistries from non-rechargeable battery chemistries. Further, the present invention allows for various chemistries to be drained to their optimal cutoff point or voltage, thereby ensuring a battery life intrinsic to the battery chemistry.